1. Field of the Invention
The present invention generally relates to a rotation control circuit of a fan and, more particularly, to a rotation control circuit of a fan that is capable of controlling a forward/backward rotation of the fan.
2. Description of the Related Art
Cooling fans are often equipped in electronic devices for heat dissipation. During the operation of a cooling fan, the cooling fan rotates in a cooling direction (clockwise or counterclockwise) to draw the external cool air into the electronic devices for heat exchange. However, the dust contained in the air may remain inside the electronic devices during the heat exchange. To clean the dust, at the moment the electronic devices are powered-on, the cooling fan would rotate in a dust dispelling direction (clockwise or counterclockwise) opposite to the cooling direction for a time period (such as 5 sec) in order to exhaust the accumulated dust from the electronic devices. After the dust exhaustion is finished, the cooling fan rotates in the cooling direction for heat dissipation of the electronic devices.
FIG. 1 shows a traditional rotation control circuit that controls forward and backward rotations of a fan for dust exhaustion and heat dissipation. The rotation control circuit comprises a motor-driving unit 91 and a micro controller 92 connected to a power supply Vcc. The motor-driving unit 91 is electrically connected to the micro controller 92 and a motor 8.
At the moment the fan begins to operate, the micro controller 92 sends a forward rotation control signal to the motor-driving unit 91 so that the motor-driving unit 91 may control the motor 8 to rotate in the dust dispelling direction for dust exhaustion.
After the time period where the dust exhaustion has been performed, the micro controller 92 sends a backward rotation control signal to the motor-driving unit 91 so that the motor-driving unit 91 may control the motor 8 to rotate in the cooling direction for heat dissipation.
Generally, the traditional rotation control circuit of the fan has a cost disadvantage as it requires the utilization of the expensive micro controller 92 for generating the forward and backward rotation control signals. Therefore, a need for cost reduction exists.